Bio-Inspired Miniature Direction Finding Acoustic Sensor

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Abstract

A narrowband MEMS direction finding sensor has been developed based on the mechanically coupled
ears of the Ormia Ochracea fly. The sensor consists of two wings coupled at the middle and attached
to a substrate using two legs. The sensor operates at its bending resonance frequency and has cosine
directional characteristics similar to that of a pressure gradient microphone. Thus, the directional
response of the sensor is symmetric about the normal axis making the determination of the direction
ambiguous. To overcome this shortcoming two sensors were assembled with a canted angle similar to
that employed in radar bearing locators. The outputs of two sensors were processed together allowing
direction finding with no requirement of knowing the incident sound pressure level. At the bending
resonant frequency of the sensors (1.69 kHz) an output voltage of about 25 V/Pa was measured. The
angle uncertainty of the bearing of sound ranged from less than 0.3° close to the normal axis (0°) to
3.4° at the limits of coverage (±60°) based on the 30° canted angle used. These findings indicate the
great potential to use dual MEMS direction finding sensor assemblies to locate sound sources with high
accuracy.

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